Plant parasitic nematodes cause serious economic damage to many agricultural crops around the world. The nematodes in this group are microscopic worms and are, in general, obligate parasites of plants. They feed mostly on the roots of host plants; however, several genera are known to parasitize above-ground parts including stems, leaves and flowers as well. Almost all the plant species of economic importance are susceptible to infection by some species of nematodes (notable exceptions are in the marigolds and asparagus). For example, root knot nematodes (RKN), (Meloidogyne spp.) are capable of parasitizing more than 3,000 species of crop plants. These plants include agronomic crops, vegetables, fruits, flowering trees and shrubs. Nematodes reportedly cause crop loss of more than six billion dollars in the United States alone and more than one hundred billion dollars around the world.
The symptoms due to parasitic nematode injury vary widely depending on the plant host, the nematode species, age of the plant, geographical location and climatic and external environmental conditions. In general, an overall patchy appearance of plants in a field is considered indicative of nematode infestation. More specifically, nematode injury results in galling of the roots (abnormal swelling in the tissue due to rapid multiplication of cells in the cortical region) caused by species of root knot (Meloidogyne spp.) and cyst (Heterodera spp.) nematodes, lesions (localized, discolored areas) caused by lesion nematodes (Pratylenchus spp.), suppression of cell division resulting in stubby roots (Trichodorus spp.), growth abnormalities including crinkling or twisting of above-ground parts (Aphelenchoides spp.), and even cell necrosis (death) in some cases. Plant parasitic nematodes may be endoparasitic in nature, as in the case of the root-knot and lesion nematodes, or ectoparasitic as in the dagger nematode (Xiphinema spp.) and lance nematode (Hoplolaimus spp.). Nematodes can be vectors of plant viruses and are also known to induce disease complexes predisposing plants to infection by other plant pathogenic fungi and bacteria.
Chemical nematocides, either soil fumigants or non-fumigants, have been in use for many years and are among the few feasible options for countering nematodes. At present, repeated applications of synthetic chemicals to the ground are required prior to planting the crop. These chemicals are extremely toxic to organisms besides nematodes and many of them may pose serious threats to the environment. With the renewed emphasis on clean water and air by environmental groups and governmental agencies, and the detection of many of these active ingredients or the metabolites thereof in ground water and several non-target organisms, there has been serious concern as to the manufacture and/or use of these chemicals. One of the most effective, economical, and widely used nematocides, DBCP (1,2-dibromo-3-chloropropane), found in ground water has been judged to induce male sterility and possible carcinogenesis. Another widely used chemical, EDB (ethylene dibromide), has also been found in ground water.
Yet another very common insecticide-nematocide, aldicarb (2-methyl-2-(methylthio)-propionaldehyde-O-(methylcarbamoyl)oxime), has been found to be acutely toxic. Aldicarb has been found in ground water in several regions of United States. Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) and 1,3-D (1,3-dichlorpropane), two very commonly used nematocides, are under special review by the EPA because of their avian toxicity and possible carcinogenic effects. More recently, the decision by the EPA to limit and eventually discontinue the use of the soil fumigant, methyl bromide, for agricultural purposes presents a threat to the efficiency and quality of agricultural production in the United States.
Natural isolates such as N-acetyl-D-glucosamine, which may be derived from microorganisms which are the waste products of industrial fermentation processes, have been disclosed as nematocidal in U.S. Pat. No. 5,057,141.
Biopesticides have been developed as an alternative to chemical pesticides. They are obtained by fermentation and can be used either as crude biomass or purified. Typically, fermentations are carried out at temperatures in the range of 20-40° C. For example, submerged fermentation at 28-30° C. of Paecilomyces fumosoroues fungal isolate ATCC No. 20874 produces fungal biomass for control of nematode infestation as disclosed in U.S. Pat. No. 5,360,607; whole fermentation broth from fermentation at 28° C. of Streptomyces thermoarchaensis NCIB 12015 is disclosed as nematocidal in U.S. Pat. No. 5,182,207; fermentation broth obtained from fermentation of Streptomyces cyaneogriseus noncyanogenus NRRL 15773 at 28° C. is effective against nematodes as disclosed in U.S. Pat. No. 5,439,934; and fermentation broth obtained by fermentation of the fungus Myrothecium verrucaria at temperatures of from 25 to 30° C. is disclosed as nematocidal in U.S. Pat. No. 5,051,255.
However, there is still a need for the development of new and effective nematocides. Plants were suggested as a source of effective pesticidal compounds as many plant essential oils exhibit antimicrobial, insecticidal, fungicidal, and herbicidal activity. They have been applied as pesticides for pest, disease and weed management.
Plant essential oils which do not present any known risk to humans or to the environment are qualified for an exemption as minimum risk pesticides and are listed in the 40 C.F.R. §152.25 (b). However, high volatility, phytotoxicity and low water solubility of some oils have limited their use in crop protection.
One plant essential oil used in agricultural applications is ProGuard® 30% Cinnamaldehyde Flowable Insecticide, Miticide, and Fungicide. See U.S. Pat. Nos. 6,750,256 B1 and 6,251,951 B1. However, a downside of this commercial product is that it contains the chemical preservative o-Phenylphenol.
Nematicidal activity of plant essential oils were reported, among others, by Y. Oka (Nematology, Vol. 3(2), pp. 159-164, 2001) and R. Pandey (J. Phytopathology 148, 501-502 (2000)). Essential oils of some plants and their components have been tested for nematicidal activity in vitro and in soil. Some plant essential oils which were determined to have nematicidal activity include essential oils of applemint (Mentha rotundifolia), caraway (Carum carvi), fennel (Foeniculum vulgare), oregano (Origanum vulgare), Syrian oregano (Origanum syriacum), and wild thyme (Coridothymus capitatus). Also, it was reported that aromatic and aliphatic aldehydes, including cinnamic aldehyde (also known as cinnamaldehyde) possess strong nematicidal activity in vitro. For example, U.S. Pat. No. 6,251,951 B1 demonstrates that cinnamaldehyde has nematicidal activity in the presence of 2% Tween 80 and 6% NaHCO3 vehicle.
Accordingly, there is a need to develop more potent, yet safe and easy-to-use formulations to improve the biological effectiveness of nematicidal plant essential oils for agricultural applications.